Temperature transmitters typically use either a resistance thermometer device or a thermocouple as a means for measuring the temperature of the medium in which they are immersed. If a resistance thermometer device is used, the temperature transmitter must convert the change in resistance of the device, as the temperature changes, to voltage. However, if a thermocouple is used, no change in its output is needed because the thermocouple produces voltage directly. In either case, the resulting voltage is non-linear. Because of this non-linearity, errors of up to several percent of full scale occur with the present temperature transmitters.
In many cases, the errors caused by this non-linearity are not corrected, especially if the system involved does not require extreme accuracy. In other cases, the errors must be corrected in succeeding portions of the control system by relatively complex electronic techniques which are quite costly. Because of this, it has become desirable to develop a simple, inexpensive electronic means which can be used for correcting the non-linear voltage response of both resistance thermometer devices and thermocouples.